There has been a proliferation of smart key systems for vehicles. A vehicle provided with a smart key system transmits a signal requesting a reply including an ID, in response to, for example, a touch of a door handle or operation of an engine start switch by a user. A key transmits its ID in reply to the signal. The system checks the ID returned by the key against the master ID stored in an onboard device, and permits the door to unlock or the engine to start if the ID is validated. Alternatively, an onboard device may transmit polling signals reaching the vicinity of the vehicle periodically without operation by a user.
For example, Patent Literature 1 discloses a smart key system for preventing theft of a vehicle more reliably. The smart key system includes a device to determine whether an occupant intends to continue driving. When a mobile device is away from a vehicle and if it is determined that an occupant having no mobile device intends to continue driving, the system permits the internal combustion engine to restart.
Such smart key systems may be deceived by a method of theft that may be called a relay attack, as exemplified in FIG. 11. In this technique, criminals A and B are located between a vehicle and its owner, who is away from the vehicle. The owner carries a smart key. The criminals A and B carry radio wave relays.
In such a condition, a request signal (a polling signal) transmitted by the vehicle is relayed by the relays carried by the criminals A and B to reach the owner. Although this type of request signal (polling signal) typically has a reach range that is limited to the vicinity of a vehicle, the relays carried by the criminals A and B enable the request signal to reach the owner. In reply to the request signal, the smart key carried by the owner of the vehicle transmits an RF signal including an ID code that is unique to the key and stored therein.
The RF signal transmitted by the key has a relatively long reach range. Upon arrival of the RF signal at the vehicle, the vehicle checks the ID included in the received RF signal against the master ID stored in the vehicle (for authentication). Since the RF signal is transmitted by the smart key carried by the owner, the verification is of course successful. This permits a door of the vehicle to unlock. The criminals can gain entry into the vehicle in this manner.
Then, repeating the similar procedure after the entry of the criminal A into the vehicle produces a successful result of the verification inside the cabin, permitting the engine to start. This allows the criminals to drive away the vehicle. The above brief description pertains to a relay attack.
There is a demand for effective measures against such a relay attack. An effective method to reduce damage caused by a relay attack may include determination whether a mobile device is in the vicinity of a vehicle. With such a measure provided, damage caused by a relay attack can be reduced effectively by permitting a door to unlock or an engine to start if it is determined that a mobile device is in the vicinity of a vehicle, and by prohibiting the door from unlocking or the engine from starting if it is determined that the mobile device is not in the vicinity of the vehicle.